In the field of silver halide photographic materials, particularly for photographing, photographic materials having high sensitivity, an ISO sensitivity of at least 100 as in ISO 400 (Super HG-400 manufactured by Fuji Photo Film Co., Ltd.) and excellent graininess, sharpness and preservability have been heretofore desired.
As examples of means for improving sharpness, couplers which undergo a coupling reaction with an oxidation product of a developing agent to produce a cleaved compound which is in turn oxidized with a second oxidation product of a second developing agent to release a development inhibitor containing a timing group are disclosed in JP-A-61-231553 and JP-A-61-240240 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"). However, there are disadvantageous as the couplers release development inhibitor at an inappropriate rate, leaving to be desired improvement in sharpness, preservability, etc., of the light-sensitive material.
As examples of compounds which improve sharpness without deteriorating the preservability of light-sensitive materials, compounds which imagewise release a development inhibitor via two or more timing groups are described in JP-A-60-218645, JP-A-60-249148 and JP-A-61-156127 and U.S. Pat. No. 4,861,701. However, these compounds do not provide a satisfactory improvement in sharpness and graininess due to an inappropriate speed (timing) of releasing development inhibitor or the excessively great dispersibility of the development inhibitor thus released. Most of the light-sensitive materials comprising said compounds are disadvantageous in that when allowed to stand for a prolonged period of time before development following exposure to light or when exposed to elevated temperature and high humidity, the result is a rise in fogging and a drop in sensitivity.
European Patent Publication 348,139 discloses couplers capable of releasing a development inhibitor in a specified structure such that sharpness can be improved without heightening interimage effect. Although the couplers enable some improvement in sharpness, the couplers are disadvantageous in that the speed of releasing a development inhibitor can be hardly controlled, leaving to be desired improvement in sharpness and causing some fluctuation in photographic properties with time between exposure and development, temperature and humidity.